Method for the production of cast iron

ABSTRACT

The invention relates to a process for incorporating additives in molten metal by bottom addition so as to ensure exposure of the additive to the molten metal at a predetermined time and to avoid premature and possibly dangerously violent reaction between the metal and the additive. The additive is placed in the bottom of the ladle which is to contain the metal and is covered with a layer of an inert material which protects the additive until the cover is disturbed.

United States Patent us] Feb. 15, 1972 McCaulay et al. 1

[72] I Inventors: James L. McCallay; Jtleph I. Hols, both of Melrion House, Albert Road North,

Reigate, Surrey, England 221 Filed: Nov. 26, 1968 [21] Appl. N0.: 779,227

[30] Foreign Application Priority Date Nov. 27, 1967 Great Britain ..53,777I67 May 31, 1968 Great Britain ..26, 1 37/68 [52] U.S.Cl. ..75/51, 75/61, 75/130 [51] hit. (I (21: 7/) [58] neld olsefl'th ..75/5l,52, 130, 130 B,61,

[ Reta-emu Cited UNITED STATES PATENTS 1,522,605 1/1925 Undurraga ..75/61 X 2,089,222 8/1937 Payne ....75/61 X 3,001 ,869 9/1961 Longstreth et al ..75/130 FOREIGN PATENTS OR APPLICATIONS 13,299 5/1901 Great Britain ..75/61 898,809 6/1962 Great Britain..... ....75/ l 30 972,708 10/ 1964 Great Britain ..75/130 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-G. K. White Attorney-Woodling, Krost, Granger and Rust ABSTRACT 16 Claims, No Drawings METHOD FOR THE PRODUCTION OF CAST IRON The difficulty of obtaining a satisfactory and efficient solution of an additive to molten metal by adding to the surface of the ladle is that the alloy losses are high and heterogeneity of the final composition usually results.

Many attempts have been made to overcome these deficiencies by methods such as stirring, agitation with gases and by using lances. Other attempts have centered around providing for bottom addition of the additive by locating it in a cavity in the bottom of the ladle and covering it with a layer of a ferrous material. Such a method is described in British Specification No. 898,809. However, where a covering of ferrous material is used, the use of too heavy a covering or the use of rusty material results in chilling of the molten metal which in turn may produce casting defects when the molten metal is poured. lf insufficient ferrous metal is used as the cover there is a danger of premature reaction which can be explosive and dangerous.

We have now devised a process whereby it is possible to ensure solution of the additives in molten metal and alloys contained in a ladle or other receiving vessel and to effect solution of the additives from the bottom of the ladle or receiving vessel and thereby obtain uniform treatment of the whole of the contents of the ladle.

The process overcomes oxidation and mechanical wash of the additive in the filling of the ladle, and thus assures controlled solution without agitation, by the introduction of additives which have either a lower melting temperature than the base material, or which are volatile or explosive in nature, or which generate gas, in such a manner that the time of the reaction between base molten metal andthe additives can be controlled on a positive and precise basis.

Our invention consists of taking an ordinary refractory lined ladle such as is in common use in melting plants and foundries, and building up at least one bar of refractory material across the bottom of the ladle reaching from wall to wall. This bar or dam may preferably be from 2 to l2 inches high or more, according to the size and shape of the ladle or receiver used and the amount and kind of additive. This bar thus divides the base of the ladle into at least two compartments, one of smaller area than the other. The additive is preferably placed in the smaller compartment. The molten metalor alloy from the furnace is then directed into the larger area and away from the additive enclosure. Thus there is quickly formed a pool of molten metal which gently flows over the bar and allows it to cover the additive without agitation or disturbance.

This construction thus takes little away from the normal capacity of the ladle and enables it to be filled and effect solution of the additive from the bottom, thereby assuring homogeneity which cannot be attained when additions are made from the top of the ladle or by simply spreading loosely on the bottom of the ladle. Moreover, this invention eliminates the chance of agitation and wash that would occur if the cavity or well were made in the bottom of the ladle.

The material from which the bar or bars forming the protective chamber is made, can be chosen according to requirements, i.e., acid, basic or neutral refractories and can be in the form of bricks, or rammed shapes. The purpose of the bar or bars is to divide the bottom of the ladle into two or more chambers, and for this purpose they can be in a straight line from wall to wall or can be curved or irregular according to requirements. Where more than one bar is provided the bottom of the ladle is thereby partitioned into three or more compartments, one of which will be for the purpose of receiving the molten metal stream during filling, and the others for containing separately two or more additives according to timing and effect sought in the metal treated. If more than one bar is used, the heights of the bar may differ, thus allowing the molten metal to enter first the chamber protected by the smaller bar, and subsequently into the chambers protected by the taller bars.

Where the additive has a lower specific gravity than the molten metal with which itis to be mixed or lower in melting temperature, or is highly volatile or explosive in nature, we

have found that by covering it with a suitable solid carbonaceous material or slag fluxing material in a predetermined amount, the time required for the heat to penetrate through to the additive can be accurately controlled. For example, alkaline and rare earth metals such as Mg, Ba, Sr, Li, Ce, Na or K or alloys of these materials which melt at a lower temperature than that of molten iron or steel, and which may be explosive and difficult to alloy with iron and steel, maybe placed in the additive enclosure and if covered with graphite in an amount equal to from l0 to 60 percent of the weight according to the size and volume of the ladle, it may be filled with molten iron or steel without alloying or reacting with the alkaline earth metal or without even melting it.

Thus by controlling the amount of graphite, one can time the reaction of the additive with the molten iron or steel, so that a uniform alloy is assured and in the case of such metals as magnesium or sodium where boiling point is lower than the temperature of the molten iron, the vapors will pass through the whole of the bath and assure maximum effect with a minimum amount of additive.

Accordingly the present invention provides a process for the treatment of molten metals by the incorporation of additives in the molten metal wherein the molten metal is introduced into a container having at least one partition across its floor defining two or more compartments, one of which compartments being of proportions suitable to receive a stream of molten metal tapped into the ladle without excessive splashing and at least one other compartment initially containing an additive covered overall with a layer of granular or powdered carbonaceous or slag fluxing base material, the stream of molten metal entering the container being directed in to the compartment or compartments proportioned to receive the metal without excessive splashing.

The invention also provides a metallurgical ladle for use in the process which comprises a metallurgical ladle provided on its floor with one or more partitions dividing the lower portion of the ladle into two or more compartments.

In a modification of the process of the invention the additive or additivesare mixed with graphite or other carbonaceous material, calcium carbide, limestone or fluxes or slag-forming substances or mixtures thereof in an amount ranging from 10 to percent by weight based on the weight of the additive and with or without a covering of carbonaceous'or slag fluxing base material.

The invention is illustrated by the following example.

EXAMPLE 1 As an example of the process of the invention, we took l4 percent Mg.FeSi alloy and placed 15 lbs. in granular form in the additive enclosure in a l-ton ladle. The alloy was then covered with 5 lbs. of granular graphite and 1 ton of molten cast iron was then tapped into the metal-receiving enclosure of the ladle. it took 4 minutes to fill the ladle from the melting furnace. Du 'ng the intervening period of time taken to fill the ladle the 14 percent magnesium ferro silicon alloy lay undisturbed After the adle was full it was removed from the casting pit, which took approximately 2 minutes, when reaction of the Mg. alloy took place in a gentle manner and without the usual display of pyrotechnics.

The iron on testing was completely nodular, the tensile strength was increased from 12 tons per square inch in the original iron to 42 tons p.s.i. after treatment.

In addition to graphite, other materials or mixtures of materials may be used, such as for example calcium carbide or desulphurizing fluxes such as limestone and fluorides or slag or mixtures of these materials.

Further if the covering of graphite, limestone mixture, calcium carbide, or slag is too thick, say more than 20 mm. or so, according to size and volume of the ladle, itmay be found'that the molten metal percolates the upper layers of the covering material and forms a solid crust of iron contaminated with the covering material and prevents the reaction taking place. It is for this reason, that we have found it desirable to control the thickness of covering material to an amount varying from -60 percent of weight of the additive. For example, a covering comprising a mixture of three parts of graphite (coarsely crushed approximately 2 mm.; using 20 percent by weight of the nodular additive, works very well for a l-ton ladle. For smaller ladles, depending on size and shape the amount required is generally under 20 percent. For larger ladles over 1 ton, the amount will vary according to the composition of the molten metal, its temperature, the size and shape of the ladle as well as the grading of the graphite and calcium carbide.

The explanation of the mechanism by which a covering material such as graphite, which is much lighter than molten metal remains at the bottom ofthe ladle until it is full, but also prevents the low melting point additive under it from reacting or fusing with the iron, is incompletely understood. However, it is thought that when the molten metal flows over the covering layer a gas film is formed which inhibits heat transfer from the molten iron to the additive for a period of time related to the thickness of the covering layer and its composition.

If a quick reaction is necessary the quantity is reduced; ifa retarded reaction is required it is increased. By this means, the timing of the reaction can be adjusted precisely, according to the temperature and quantity of molten metal to be treated and according to the holding time required in service before using.

To illustrate, both graphite and ferrous coverings are materials of good thermal conductivity, yet a ferrous covering over the additive does not permit the practice of this invention, or control ofthe violence of the reaction.

By using a covering of three parts of graphite and one part of calcium carbide in a rib partitioned ladle, the reaction can be delayed so long as the molten iron retains adequate temperature. Further such a procedure enables a positive control and consistent production of castings or superior physical properties.

The process of the present invention can, with advantage, be combined with the concept of the invention of our British Pat. No. 972,708.

British Pat. No. 972,708 describes and claims a method of manufacturing cast iron to a controlled form of flake or nodular structure wherein one or more additives are placed in an additive container through which gas can pass, the additive container being arranged in a vessel containing molten cast iron, and an inert gas is blown into the vessel through the addi tive container. One effect of blowing inert gas through the molten metal in the container is to agitate the molten metal and, with suitable choice of additive, to effect chemical changes in the composition ofthe molten metal.

In accordance with the process of the present invention gas injection is combined with treatment of the metal by the inclusion of additives as described above.

In this embodiment of the process the container for the molten metal is provided on its floor with one or more partitions defining two or more compartments and the container is also provided in one of the compartments or in its wall with a porous plug externally connected to a supply of the desired gas. The additive or additives together with cover layer are placed in one or more compartments of the ladle and metal tapped in as described above. Gas injection through the porous plug can then take place during and or after the reaction of the metal with the additive.

Where the porous plug is situated in a compartment on the ladle floor the compartment can also contain an additive on top of the porous plug and the additive, if it is of a lower specific gravity than the molten metal or if it is an additive which reacts violently with the molten metal, can be covered with a layer ofa material of a nature and ofa thickness to ensure that reaction between the molten metal and the additive will not take place until the cover layer is disturbed. In this embodiment, when the ladle is full gas injection can be started which disperses the additive from the porous plug compartment into the molten metal, if necessary after disturbance of the cover layer by the stream of gas. This operation can be timed to take place at any time before, during or after reaction of the other additive or additives with the molten metal.

In another embodiment of the invention it has been found that the stream of gas from the porous plug can be used as the sole means of disturbing a cover layer to expose an additive to the molten metal. In this case the porous plug is situated in a compartment in the ladle floor which compartment also contains the desired additive. The additive is then covered with a layer of inert material which, in this embodiment, does not need to have the properties of predetermined heat transfer referred to in connection with other embodiments of the invention. Metal is then tapped into the ladle in such a way that the cover layer of the additive is not disturbed. At the desired time gas is passed through the porous plug which results in disturbance of the cover layer, exposure of the additive to the molten metal and the dispersal of the additive in the molten metal by the chemical reaction taking place assisted by the agitation caused by the flow of gas through the metal.

In yet another embodiment of the invention, again utilizing the basic principle of disturbance of the protective cover layer over an active additive situated at the bottom of the ladle, a refractory stopper rod is placed in the ladle, the lower end of the rod resting in the compartment destined to receive the additive. The additive and an inert cover layer are then placed in the compartment as previously described and metal is tapped into the ladle without disturbing the cover layer. At the desired time the refractory stopper rod is raised which allows the molten metal access to the additive resulting in a reaction which by its effect completes the disturbance of the remaining cover layer. This embodiment of the invention can, of course, be used in conjunction with gas injection using a porous plug or using a lance for gas injection.

Further, if desirous, and according to operating conditions, any other obvious means of physical disturbance may be employed to pierce and mechanically break the cover crust cxposing the reagent to the molten metal. As examples refractory or refractory coated rods or steel bars may be used for this purpose.

Any two or more embodiments ofthe invention can be combined to produce a plurality of treatments in one ladle of molten metal, each treatment being effected at a predetermined time and therefore in a desired sequence. In addition any of the embodiments of the invention can be operated in conjunction with the addition of an additive to the surface of the molten metal which is incorporated in the metal as a result of the agitation caused by the particular method or methods of the invention employed.

,The invention is further illustrated by the following additional examples.

EXAMPLE 2 Twelve pounds of a magnesium ferro silicon alloy (containing 9 percent magnesium) was placed on the floor ofa l0 cwt. capacity refractory lined ladle which was fitted with a porous gas inlet member connected to a gas supply. The additive was placed directly on top of this porous member, and covered with a mixture comprising three parts graphite to one part granular calcium carbide-in total equivalent to 30 percent by weight of the additive or supplying an adequate cover of approximately five-eighths-inch thickness.

Ten hundredweights of cupola melted iron was tapped into the ladle directing the metal stream away from the covered additive. The metal rose over the aggregate cover without disturbance or wash. It took 2 minutes to collect this quantity of metal, during which time the highly reactive magnesium alloy remained undisturbed on the ladle bottom. The gas supply to the porous member was then turned on at a pressure of 10 psi. and at a rate of 60 cu.ft./hour until the additive reaction commenced-the period being approximately 10 seconds. The magnesium reaction continued at a controlled EXAMPLE 3 A large l0-ton capacity ladle was used to treat 8 tons of ordinary cupola iron. The ladle used had its refractory floor subdivided into three compartments formed by 3-inch high refractory bars. Porous plug assemblies as described previously having been fitted to the ladle bottom, positioned one in each compartment.

In this case the metal was required to be nodular cast iron containing 0.5 percent molybdenum. To achieve this using a high sulphur base metal (012 percent sulphur) it is of course economically advantageous to remove a large proportion of the sulphur prior to introducing costly nodularising reagents which interreact with the sulphur compounds resulting in poor magnesium recoveries. To effect sulphur reduction'one additive compartment was charged with 1 percent of a mixture comprising calcium silicide and sodium fluoride in the ratio of 1226 based on the metal treatment weight.

The second compartment was charged with 1.2 percent ofa magnesium ferro silicon alloy (containing 14 percent magnesium).

The additions in both these compartments were covered with the protective aggregate mixture used in Example 1 in an amount of 50 percent by weight of the additive, affording approximately a l-inch layer of protective aggregate.

An addition of 0.75 percent granular ferro molybdenum alloy was finally placed in the third compartment. Since this latter alloy is highly refractory and normally presents solution problems, no cover was applied. The metal from the cupola was directed into the compartment containing the ferro molybdenum alloy. The metal levelgradually rose over the compartment partition and gently flowed over into the other two compartments containing the highly reactive additives without agitation or wash disturbing the cover aggregate.

When the tap was complete, the gas supply to porous member containing the ferro molybdenum was turned on at a pressure of 25 psi. and a flow rate of 120 cu.ft./hr. The resultant agitation and turbulence created to ensure maximum solution and recovery of the molybdenum alloy and complete homogeneity throughout the bath of metal did not disturb the protective covers in the other two compartments. After 1 minutes agitation the gas source was disconnected and switched to the porous member in the compartment containing the sodium fluoride calcium silicon mixture. When the protective cover was now disturbed, the interreaction between the sodium salt and the calcium silicide liberated nascent sodium vapor which effected sulphur removal in the ladle to a residual level of 0.01 percent. The mild agitation created by the liberation of the sodium vapor was sufficient in itself to ensure homogeneity and the gas supply to this porous member was shut off once the reaction commenced.

Finally the gas supply to the porous device serving the compartment containing the magnesium-bearing additive was switched on until the reaction commenced, after which the supply was turned off. The magnesium reaction progressed as described in the previous example.

By this treatment the properties of the iron had been changed from 13.4 tons per square inch to 47.8 tons per square inch with 3 percent elongation.

In addition to the basic concept ofthis application it is readily possible to effect a series of metallurgical treatments by modest, inexpensive alterations to ladle designs such as the multicompartment ladle employed in the above example and also to incorporate several porous plug units for purposes of homogeneity and economics or for purposes of timing the solution of different additives according to the type. nature, and properties of the metal or alloy to be used.

The process can be utilized for a wide range of treatments of irons, steels, and nonferrous alloys for the purposes of deoxidizing, cleansing, desulphurizing, nodularizing, alloying, degassing, inoculation, grain refinement, or modification of composition structure and properties.

EXAMPLE 4 To reduce the manganese content of iron, the following mixture was added to the floor of a l-ton ladle fitted with a porous plug as described:

KClO: powder 2 percent by weight of the metal,

Fine silica sand 4 percent by weight of the metal.

This mixture having been placed over the porous member was covered with a l-inch layer of granular limestone. The iron containing 0.6 percent manganese was tapped into the ladle but not directly onto the protected additive. The iron flowed over the cover with no disturbance. When the tap was complete the gas supply was turned on at 10 p.s.i. pressure until the oxidizing reaction commenced when it was turned off. The additive reaction continued for approximately 1 /2 minutes.

The manganese content after treatment was 0.12 percent.

EXAMPLE 5 The object in this case was to purify, degas aluminum alloy castings.

A two-compartment ladle was used and 1 lb. of hexachloroethane was placed in one compartment and covered with a three-fourths-inch layer of powdered limestone 30 mesh).

Six hundred pounds of the aluminum alloy was tapped into the empty partitioned zone without disturbing the protective cover. The gas supply to the porous device in the ladle bottom was switched on for 10 seconds and the reaction proceeded liberating chlorine gas which purged the melt of harmful hydrogen gas and the agitation created washed slag and oxide inclusions to the surface of the melt where they were skimmed clear.

In other instances it may be preferable to add one additive reagent oralloy to the metal surface and utilize gas agitation from one or more of the porous members located in one or more compartment in the ladle bottom thus ensuring maximum efficacy and homogeneity; this is a pretreatment prior to disturbing a reactive additive previously charged to another compartment or partitioned zone as has been described.

What we claim is:

1. A process for the treatment of molten metals by the incorporation of additives in, the molten metal wherein the molten metal is introduced into a container having at least one partition across its floor defining at least two compartments, one of which compartments being of proportions suitable to receive a stream of molten metal tapped into the ladle without excessive splashing and at least one other compartment initially containing an additive covered overall with a layer of granular or powdered carbonaceous or slag iluxing base material, the stream of molten metal entering the container being directed into the compartment proportioned to receive the metal without excessive splashing.

2. A process as claimed in claim 1 wherein the container has a flat floor and is partitioned into at least two compartments by means of a raised refractory slab.

3. A process as claimed in claim 1 wherein the partition is a bar of refractory material built up on the floor of the container.

4. A process as claimed in claim 1 wherein the container is partitioned to form at least three compartments on its floor and at least two additives are used, each additive being contained separately in a different compartment, the heights of the partitions forming the compartments being arranged to differ so that molten metal enters the compartments in a predetermined order.

5. A process as claimed in claim 4 wherein one of the additives is covered as defined and other additives present in other compartments are not provided with a cover.

6. A process as claimed in claim 1 wherein the additive is covered with graphite or other carbonaceous material, calcium carbide, limestone or fluxes or slag forming materials or mixtures thereof in an amount ranging from to 60 percent by weight based on the weight ofthe additive.

7. A modification of the process claimed in claim 1 wherein the additive is mixed with graphite or other carbonaceous materials, calcium carbide, limestone or fluxes or slag forming substances or mixtures thereof in an amount ranging from 10 to 100 percent by weight based on the weight of the additive.

8. A process as claimed in claim 1 wherein the additive comprises a nodularizing agent.

9. A process as claimed in claim 1 wherein the container is provided with a porous plug connected externally of the container to a supply of gas, the plug being situated in the container and gas is blown through the plug into the molten metal.

10. A process as claimed in claim 9 wherein the plug is situated in a compartment on the ladle floor which compartment contains an auxiliary additive which may be covered with a material in such a way that reaction of the additive and the molten metal will not take place unless the cover is disturbed, and, after filling the container gas is blown through the plug to disturb the cover and to distribute the auxiliary additive in the molten metal.

11. A modification of the process as claim in claim 10 wherein at least one primary additive is contained in at least one compartment provided with a porous plug and the primary additive is covered in such a way that reaction between the additive and the metal will not take place until the cover is disturbed, and, after filling the container, gas is blown through the plug, in a desired sequence where more than one plug is used, to disturb the cover and to expose the primary additive to the molten metal and to distribute it in the molten metal.

12. A modification of the process as claimed in claim 1 wherein the container is provided with a refractory stopper rod the lower end of which rests in a compartment in the ladle floor, the desired additive is filled into the compartment and is covered with an inert cover material, molten metal is tapped into the ladle in such a way that the cover layer is not disturbed and, at a predetermined time, the refractory stopper rod is withdrawn exposing the additive to the action of the molten metal.

13. A modification of the process as claimed in claim 1 wherein the inert cover is disturbed by direct mechanical action, for example by piercing or breaking the cover layer.

14. A process as claimed in claim 1 wherein, in addition, gas is injected into the molten metal by means ofa lance inserted beneath the surface ofthe molten metal.

15. A modification of the process as claimed in claim 9, wherein the inert cover is disturbed by direct mechanical action, for example, by piercing or breaking the cover layer.

16. A process as claim in claim 9, wherein, in addition, gas is injected into the molten metal by means of a lance inserted beneath the surface of the molten metal. 

2. A process as claimed in claim 1 wherein the container has a flat floor and is partitioned into at least two compartments by means of a raised refractory slab.
 3. A process as claimed in claim 1 wherein the partition is a bar of refractory material built up on the floor of the container.
 4. A process as claimed in claim 1 wherein the container is partitioned to form at least three compartments on its floor and at least two additives are used, each additive being contained separately in a different compartment, the heights of the partitions forming the compartments being arranged to differ so that molten metal enters the compartments in a predetermined order.
 5. A process as claimed in claim 4 wherein one of the additives is covered as defined and other additives present in other compartments are not provided with a cover.
 6. A process as claimed in claim 1 wherein the additive is covered with graphite or other carbonaceous material, calcium carbide, limestone or fluxes or slag forming materials or mixtures thereof in an amount ranging from 10 to 60 percent by weight based on the weight of the additive.
 7. A modification of the process claimed in claim 1 wherein the additive is mixed with graphite or other carbonaceous materials, calcium carbide, limestone or fluxes or slag forming substances or mixtures thereof in an amount ranging from 10 to 100 percent by weight based on the weight of the additive.
 8. A process as claimed in claim 1 wherein the additive comprises a nodularizing agent.
 9. A process as claimed in claim 1 wherein the container is provided with a porous plug connected externally of the container to a supply of gas, the plug being situated in the container and gas is blown through the plug into the molten metal.
 10. A process as claimed in claim 9 wherein the plug is situated in a compartment on the ladle floor which compartment contains an auxiliary additive which may be covered with a material in such a way that reaction of the additive and the molten metal will not take place unless the cover is disturbed, and, after filling the container gas is blown through the plug to disturb the cover and to distribute the auxiliary additive in the molten metal.
 11. A modification of the process as claim in claim 10 wherein at least one primary additive is contained in at least one compartment provided with a porous plug and the primary additive is covered in such a way that reaction between the additive and the metal will not take place until the cover is disturbed, and, after filling the container, gas is blown through the plug, in a desired sequence whEre more than one plug is used, to disturb the cover and to expose the primary additive to the molten metal and to distribute it in the molten metal.
 12. A modification of the process as claimed in claim 1 wherein the container is provided with a refractory stopper rod the lower end of which rests in a compartment in the ladle floor, the desired additive is filled into the compartment and is covered with an inert cover material, molten metal is tapped into the ladle in such a way that the cover layer is not disturbed and, at a predetermined time, the refractory stopper rod is withdrawn exposing the additive to the action of the molten metal.
 13. A modification of the process as claimed in claim 1 wherein the inert cover is disturbed by direct mechanical action, for example by piercing or breaking the cover layer.
 14. A process as claimed in claim 1 wherein, in addition, gas is injected into the molten metal by means of a lance inserted beneath the surface of the molten metal.
 15. A modification of the process as claimed in claim 9, wherein the inert cover is disturbed by direct mechanical action, for example, by piercing or breaking the cover layer.
 16. A process as claim in claim 9, wherein, in addition, gas is injected into the molten metal by means of a lance inserted beneath the surface of the molten metal. 